This invention relates to pellet implanters and in particular to hand held implanters for implanting medicinal pellets and the like in animals.
Pellet implanters are widely used in livestock handling operations to insert solid or semisolid medicaments such as growth stimulating hormones into animals to be treated. Pellets containing growth stimulating hormone are typically injected into the ears of domesticated animals since the ears are commonly discarded in the slaughtering process thereby preventing unabsorbed residues from ending up in food products intended for human or domestic animal consumption.
Typical implanter devices comprise hand held instruments built of a size consistent with the size of the animal. The pellets are normally implanted while an animal is confined in a chute. An ear is grasped in one hand, and an implanter device having a large bore hypodermic needle is used to puncture the hide to enable a pellet dose to be injected between the hide and the next layer of tissue in the ear. The implanting must be done carefully to ensure that the pellets are properly placed and that no pellet remains in the puncture in the hide, which could result in an infection. At the same time, the procedure must be carried out quickly since the animals are not entirely cooperative and may shake their heads to free the held ear.
Further complicating matters is that other procedures may be occurring at the same time as the implanting operation while the animal is confined, such as ear tagging, branding, veterinary inspections or procedures, or the like, which may further excite the animal.
The great majority of implanter devices employ manual gripping force on a trigger and a hand grip of such a device to propel an impeller through a pellet holding device or a magazine to drive the pellets through the needle and into the space formed by operation of the trigger to return the impeller to its retracted position when the trigger is released. With such an arrangement, pellet implanting is complicated by the need to coordinate withdrawal of the needle as the pellets exit the needle. Such complexity of motion coupled with fatigue from using grip strength to eject the pellets can result in mistakes, such as lodging a pellet in the hide puncture or some of the pellets being ejected onto the ground.
A number of implanter devices use multiple pellet dose magazines to hold a plurality of pellet doses. Each pellet dose usually consists of a plurality of small pellets of a measured drug dosage which are positioned in an in-line orientation within a cylindrical chamber of the magazine. The magazine is a strip having a plurality of such chambers arranged in parallel relation, such as by being connected by webs between the chambers. Although some implanters are known to have magazines which advance to the next magazine chamber each time an implant operation occurs, many implanters require manual advancing of their magazines. Such manual advancing of the pellet magazine requires that the person performing the implanting operation remember to advance the magazine after each operation. If the magazine is not advanced, no pellets will be injected.
U.S. Pat. No. 5,522,797 discloses an implanter in which the impeller is manually retracted against the driving force of a spring and then locked in position with a latch mechanism, thereby storing the spring force. Squeezing or pivoting of an associated trigger, releases the latch mechanism which resiliently drives the impeller through an aligned magazine chamber and propels the pellet or pellets in the magazine into the needle. As the needle is withdrawn from the portion of the animal into which it has been inserted, the pellets are urged out of the end of the needle and into the hole formed by the needle. Although the implanter disclosed in U.S. Pat. No. 5,522,797 overcomes many of the problems associated with prior art implanters, the user must still manually retract the impeller after each use which can slow down the process of implanting medicaments in a large number of animals such as may be necessary in large feed lots.
There remains a need for an implanter which permits rapid, successive implantation of medicaments in a large number of animals with minimal manual effort.